This invention relates to blends of ethylene vinyl alcohol copolymer with an amorphous polyamide component and their use as a barrier layer in thermoformed multilayer containers and other applications.
Blends of ethylene vinyl alcohol polymers with polyamides in general are known, and have been used in packaging applications as barriers to inhibit the passage of atmospheric oxygen or other gases.
European patent application 0 305 146 discloses a blend of about 70 to about 95 percent by weight of an ethylene vinyl alcohol copolymer having a copolymerized ethylene content of about 20 to about 60 mole percent and a degree of saponification of at least about 90%, and about 5 to about 30 percent by weight of an amorphous polyamide. The composition is useful as a barrier layer in thermoformed containers.
European patent application 0 309 095 discloses a blend of about 50 to about 95 weight percent of an amorphous polyamide and about 5 to about 50 weight percent of a vinyl alcohol polymer having a copolymerized ethylene content of 0 to about 60 mol percent and a degree of saponification of at least about 90%. The blends have oxygen barrier properties which are relatively independent of humidity. Packaging films, laminates, and containers prepared therefrom are disclosed.
U.S. patent application Ser. No. 07/301,473 discloses a blend of ethylene vinyl alcohol copolymer and a polyamide blend of about 30 to about 90 percent by weight of at least one amorphous polyamide and about 10 to about 70 percent by weight of at least one semicrystalline polyamide which is miscible with the ethylene vinyl alcohol copolymer. The blends are useful for forming films, multiple layer structures, and formed structures prepared by stretching or thermoforming such multiple layer structures.
Japanese patent application 53-49050 discloses a blend of ethylene vinyl alcohol copolymer (EVOH) with 5 to 40 weight percent polyamide. The EVOH contains 20-50 mole percent copolymerized ethylene, and is saponified at least 90%. The polyamides disclosed include a copolymer of hexamethylene diamine with isophthalic and terephthalic acids, in mole ratios of 100/0 to 50/50. The blend is formed into a film, which possesses gas barrier properties. The barrier performance of the film is purported not to decline even in highly humid atmospheres.
U.S. Pat. No. 3,726,034 discloses mixtures of 70-99% polyamide and up to 30% of a hydroxyl containing polyolefin. The polyamides "consist of linear unbranched polymer chains containing no additional functional groups." Exemplified are blends of nylon 6 and EVOH.
U.S. Pat. No. 4,079,850 discloses a multilayer blow molded container, which contains a layer which may be EVOH, polyamide, or various blends, providing gas barrier properties. The polyamides which are mentioned are nylon 6, nylon 66, and nylon 12.
U.S. Pat. No. 4,427,825 discloses a composition of matter useful for making films, of polyamide and 1-65% EVOH. Nylons with melting points greater than 175.degree. C. are preferred, such as nylon 11 or nylon 12.
U.S. Pat. No. 4,500,677 discloses a resin composition comprising a mixture of two EVOH resins and a polyamide resin. The ratio of the EVOH resins to the nylon resin can be between 95:5 and 5:95. Nylon 6, nylon 6,6 and other polyamides having "linear alkylene group[s]" are specifically mentioned.
Ethylene vinyl alcohol copolymer (EVOH) is commonly used in the form of a thin layer together with thicker layers of less expensive structural materials, for example, polypropylene or polyethylene terephthalate, in order to form a structure which is resistant to the passage of atmospheric oxygen or other gasses. In order to make containers or oriented films of such multilayer structures a solid phase thermoforming process is often used. However, EVOH cannot be formed at the relatively lower temperatures required for the thermoforming of many common structural materials without rupturing the EVOH layer, resulting in a loss of overall barrier performance. The present invention provides a modified EVOH composition which may be used in thermoformed multilayer structures to avoid the above mentioned problems, and without substantially sacrificing the excellent gas barrier properties of EVOH. It may also be used in other applications where stretching is required during the processing of the article, such as in shrink films.